1. Field of the Invention
The present invention relates to digital image processing, and more particularly, to an apparatus for improving the sharpness of an image, that can naturally improve the sharpness of an image without distortion by applying a 2-dimensional (D) high pass filter (2-D HPF) having an appropriate gain depending on the strength of an edge detected from a digital image.
2. Description of the Related Art
In general, an image sharpness improving technique adopts a method of strengthening the edge component (outline) of an image. For a related art edge strengthening technique improving the sharpness of an image, there exist a method of applying the same 2-D high pass filter (2-D HPF) to an entire image and applying a corresponding edge strengthening value to an original image, and a method of analyzing the characteristics of edges (outlines), applying a 2D HPF suitable for each characteristic, and applying corresponding edge strengthening values to an original image.
The related art method of applying the same 2-D high pass filter (2D HPF) to an entire image can improve the sharpness of the entire image, but applies the 2-D high pass filter to an original image regardless of the strengths of edges of the image. Accordingly, excessive strengthening is applied to a strong edge and so a ringing phenomenon that a white edge is formed in the outline region of an object may be generated, which makes the image unnatural.
In the related art method of analyzing the characteristics of edges (outlines) and applying a 2D HPF suitable for each characteristic, the directionality of an edge such as a horizontal direction, a vertical direction, and no directionality is analyzed, a 2-D HPF suitable for each directionality is generated and applied, and corresponding edge strengthening values are then applied to an input image. In this related art method, various kinds of judgment masks should be used in order to analyze the directionality of each edge, and different kinds of 2-D HPFs are required depending on the directionalities, so that a system may increase in size. Also, since this related art method does not consider the strength of an edge though having an algorithm for judging directionality, a ringing phenomenon may be generated to a strong edge portion. In addition, even when different kinds of 2-D HPFs are applied depending on the directionality of an edge, edge strengthening by the same 2-D HPF is applied to edges having the same directionality, so that it is still difficult to naturally improve sharpness.